As is well known, natural gas is a plentiful and relatively inexpensive energy product. It is widely used in a large number of industries including power generation, home heating, transportation, fertilizers, hydrogen generation as well as in the manufacture of many products.
To date, the use natural gas in the transportation industry has been generally limited to compressed natural gas (CNG) that has been utilized within internal combustion engines (ICEs). In these applications, a compressed gas tank stores the natural gas and the natural gas is delivered to the chambers of the ICE primarily through the release of pressure from the gas tank. Generally, a CNG vehicle is advantaged over gasoline type vehicles by improved emissions quality; however a CNG is disadvantaged by the overall energy density of the CNG within a compression tank. In addition, there is also a general perception amongst the public that CNG as a fuel within a compression tank is substantially more dangerous than a liquid fuel in an un-pressurized tank due to the perceived potential for explosion with a compressed gas.
Liquid natural gas (LNG) as an energy source provides a number of advantages over CNG particularly in terms of energy density. More specifically, LNG has approximately 2.4 times the energy density of CNG. Advantageously, LNG also has an energy density on a mass basis approximately 50% higher than of gasoline. However, on a volumetric basis, the energy density of LNG is about 50% that of gasoline. As such, for a given mass of LNG, the LNG stores approximately 50% more energy in comparison to an equivalent weight of gasoline.
Thus, as a form of vehicular energy, notwithstanding the volumetric disadvantage of LNG compared to gasoline, LNG is attractive as a vehicular fuel as it contains approximately 50% more energy than gasoline on a weight basis.
Moreover, as a relatively pure product that does not require the level of refining of liquid petroleum products, natural gas and LNG are also very attractive from a cost perspective.
As is known, the economics of LNG as an energy sources are complex in that many factors go into the determination of an LNG price including the base price of the natural gas, the costs of the liquefaction process, transportation and storage costs as well as jurisdictionally imposed taxes. End product capital costs of the equipment using the LNG are also a factor in the final cost of delivering the LNG energy sources to the consumer. However, with the assumption that transportation costs are a small component of the price of LNG, and that many of above costs are comparable to gasoline, the cost of LNG to an equivalent volume of gasoline is approximately 50% of that of gasoline.
In addition to the cost and bulk energy considerations of LNG compared to gasoline, there are also performance considerations associated with the use of LNG within a combustion engine.
In particular, the cryogenic state of LNG has the potential to affect the performance of combustion engines by providing effective cooling within an engine. That is, as is well known, the performance of a combustion engine can be improved by increasing the density of the incoming combustion air. By way of example, intercoolers are used to effect a cooling of combustion air entering an internal combustion engine so as to improve the combustion processes within the engine.
Furthermore, by virtue of the energy required to effect liquefaction of natural gas to LNG, LNG effectively stores energy of vaporization which on conversion from liquid to gas may be used to perform useful work.